The present invention concerns a continuous regeneration type diesel particulate filer unit for cleaning the exhaust gas by capturing particulate of a diesel engine and a regeneration control method of the same.
The restriction of discharge quantity of particulate (the PM: particulate: referred to as the PM hereinafter) discharged from the diesel engine is reinforced year by year together with NOx, CO and HC or the others. Therefore, a technique for reducing the quantity of the PM discharged outside, by capturing the PM by means of a filter called diesel particulate filer (DPF: Diesel Particulate Filter: referred to as DPF hereinafter) has been developed.
The DPF for capturing the PM includes monolith honeycomb form wall flow type filters made of ceramics, fiber filter type filters made of fiber shape ceramics or metal, or the others. The exhaust emission control device using these DPFs are installed in the middle of the engine exhaust pipe, similarly to the other exhaust emission control devices, for cleaning exhaust gas generated in the engine before discharging.
However, the filter of DPF unit for the PM capture is clogged gradually along with the capture of the PM and the exhaust pressure raises substantially in proportion to the quantity of captured the PM, thus requiring to remove the PM from the filer. Mainly three kinds of method and unit have been developed.
The first of them concerns a regeneration unit and method of the same for using two filters alternately to capture the PM in exhaust gas by one filter and regenerate by burning the captured the PM heating by the other filter through an electric heater or the like.
The second method and unit consists in using a solid filer as filter, disposing an oxidation catalyst upstream the solid filter, and treating the PM captured in the solid filter by a chemical reaction based on the oxidation catalyst.
The third method and unit consists in using a solid filter provided with catalyst and a catalyst additive agent for accelerating the burning of the PM.
Primary clogging factors of these DPF units include, in addition to smog or the like that are unburned components of the fuel and ash of burned lubricant oil.
The lubricant oil is supplied to different parts of an engine and the periphery of piston rings from a lubricant oil reservoir to circulate in the engine, and penetrates into the engine cylinder from the peripheries of piston rings and valves.
When the lubricant oil is exposed to a high temperature in the engine cylinder, calcium, zinc or other ingredients contained in the lubricant oil are not burned and remain as ash, and the ash is contained and borne by the exhaust gas and captured by the filter of a DPF unit.
Moreover, the ash captured by the filter is not burned and not removed by the filter regeneration operation or the others and accumulated in the filter even slightly. Lubricant oil leaks extremely slightly on the order of several tens of litter per ten thousand km of traveling; however, its total amount can not be neglected as the mileage increases. If the mileage attains the order of several ten thousand km or a hundred thousand km, the filter clogging due to the ash deposit and accumulation progresses, affecting the exhaust pressure before and after the filter.
On the other hand, in the DPF unit of the related art, the clogging of filter due to the PM is judged by comparing the exhaust pressure measured before and after the filter and a predetermined exhaust pressure judgment value, and it is so controlled to start the filter regeneration operation, when exhaust pressure, difference pressure, pressure ratio or the others calculated from the measured exhaust pressure exceeds the predetermined judgment value.
However, the PDF unit of the related art has a problem that the exhaust pressure raises gradually along with the increase of mileage, as the filter clogging due to ach generated from the lubricant oil is not considered, making the judgment to start the regeneration operation becomes gradually inappropriate.
Besides, the second and the third units are units for lowering the burning start temperature of the PM by the function of a catalyst such as xcex3 alumina, Pt, zeolite, or the like supported by the filter, and incinerating the PM by the exhaust gas, called xe2x80x9ccontinuous regeneration type DPFxe2x80x9d.
In case of the continuous regeneration type DPF, the temperature of exhaust gas flowing in the PDF may be increased to a temperature for activating the catalyst (par example, equal or superior to 250xc2x0 C.).
The PM cleaning mechanism in the exhaust gas is different according to engine operation areas (torque and engine speed) (C1), (C2) as shown in FIG. 17.
First, in the area (C1), carbon (C: the PM) is oxidized to carbon dioxide (CO2) through a reaction (4CeO2+Cxe2x86x922CeO3+CO2, 2CeO3+O2xe2x86x924CeO2) by catalytic action of the a filter with catalyst 4, while in the area (C2), carbon (C: the PM) is oxidized to carbon dioxide (CO2) through a reaction (C+O2xe2x86x92CO2).
Then, in the engine operation areas (torque and engine speed) (C1), (C2) as shown in FIG. 17, the PM in the exhaust gas G is cleaned continuously regenerating the filter with catalyst 4, by cleaning the PM captured by the filter with catalyst 4. It should be appreciated that though the division between these (C1) and (C2) is schematically shown in FIG. 17, there is not necessarily a clear boundary, but main reaction varies gradually.
However, for the continuous regeneration type DPF unit, in case where the exhaust gas temperature corresponding to the engine operation area (D) in FIG. 17 is low, the catalyst temperature lowers deteriorating the catalyst activity, and therefore, the aforementioned action does not occur, and the filter can not be regenerated by oxidizing the PM. Consequently, the PM continues to accumulate, clogging the filter.
Especially, during idling or low load driving, and during engine brake operation on a downhill or the others, the fuel burns hardly, and a cool exhaust gas flows into the filter with catalyst, lowering the catalyst temperature and deteriorating the catalyst activity. Moreover, the PM deposits on the filter during the driving period of time where the filter can not be regenerated.
The first object of the present invention is to provide a diesel particulate filer unit (DPF unit) allowing to judge appropriately the start timing of regeneration operation, by estimating the state of accumulation of ash generated from a lubricant oil and correcting or compensating the exhaust pressure judgment value concerning the exhaust pressure used for judging the regeneration start, with the ash accumulated estimation value, and to remove the PM efficiently, all the way preventing the filter from clogging.
The second object of the present invention to provide a DPF unit allowing to remove the PM efficiently all the way preventing securely the filter from clogging, by controlling the engine exhaust gas temperature, through surveillance of the accumulation state of the PM.
The DPF unit for achieving the first object is configured as follows.
1) A DPF unit comprising a filter for capturing particulates in the exhaust gas of a diesel engine, an exhaust pressure sensors disposed in an exhaust passage, and a regeneration control means for starting the regeneration operation of said filter, according to the judgment results based on the comparison between the exhaust pressure measured by the exhaust pressure sensors and a predetermined exhaust pressure judgment value, and regenerating said filter by removing particulates captured by said filter through combustion or chemical reaction by a catalyst, wherein said regeneration control means is configured to estimate the ash accumulated quantity of ash leaked into the exhaust gas and accumulated in said filer and to correct said exhaust pressure judgment value for judging the regeneration operation start based on said ash accumulated estimation value.
Concerning the DPF unit and its regeneration operation, as follows, there are regeneration operations corresponding respective type of PDF unit; the other PDF units or regeneration operations may by devised.
The regeneration operation used often for a PDF unit changing over a plurality of filters alternately includes an operation to incinerate particulates by turning on a heating heater disposed in the filter and heating the filer to the particulate combustion temperature or higher. Moreover, the regeneration operation for a DPF unit supporting a catalyst by the filter includes an operation for removing particulates through a chemical reaction by the catalyst, by raising the exhaust gas temperature.
Besides, the judgment based on the comparison between the exhaust pressure measured by the exhaust pressure sensors and the predetermined exhaust pressure judgment value includes manners of judgment described below, or manners of judgment by the combination thereof; however, the other judgments may be adopted provided that they use the exhaust pressure and the predetermined exhaust pressure judgment value.
One of them consists in comparing the exhaust pressure Pe measured by an exhaust pressure sensors disposed upstream the filter and a predetermined exhaust pressure judgment value Pes, and starting the regeneration operation when the measured exhaust pressure Pe exceeds the predetermined exhaust pressure judgment value Pes.
Another one consists in comparing the differential pressure xcex94Pe=Pexe2x88x92Peb between the exhaust pressure Pe measured by an exhaust pressure sensors disposed upstream the filter and the exhaust pressure Peb measured by an exhaust pressure sensors disposed downstream the filter with a predetermined exhaust pressure judgment value xcex94Pes, and starting the regeneration operation when the measured exhaust pressure xcex94Pe exceeds the predetermined exhaust pressure judgment value xcex94Pes.
Besides, there is also a judgment method for comparing the pressure ratio Re=Pe/Peb and a predetermined pressure ratio judgment value Res, in place of differential pressure xcex94Pe, and starting the regeneration operation when the measured pressure ratio Re exceeds the predetermined pressure ratio judgment value Res.
2) The aforementioned DPF unit, wherein the regeneration control means is configured to calculate the ash quantity accumulated in said filter during an engine operation state, from the torque of an engine and the engine speed, and to calculate the ash accumulated estimation value, through the cumulative computation of the calculated ash quantity.
For calculating the ash quantity Ash of combustion remaining ash of leaked lubricant oil depositing and accumulating on the filter during the operation state of an engine, from the torque Q of the engine and the engine speed Ne, a map data Mash (Q, Ne) and a function fash (Q, Ne) are prepared, and they are used. The map date Mash is to be determined beforehand from the relation between the torque Q of an engine and the engine speed Ne obtained by experiment and computation, and the ash quantity Ash to be accumulated in the filter during such engine operation state.
The ash quantity can be determine from the quantity of lubricant oil consumed according to the engine operation state, by means of experiment or computation. Besides, as an ash quantity is produced on the order of 8 g to 10 g by one (1) litter of lubricant oil, the map data Mash (Q, Ne) and the function fash (Q, Ne) can also be obtained by converting the exhaust pressure increment due to the clogging of the filter with the ash quantity, from the ash quantity.
3) The aforementioned DPF unit, wherein the regeneration control means are configured to calculate an exhaust pressure coefficient corresponding to said ash accumulated estimation value, and correct said exhaust pressure judgment value to a value determined by multiplying a reference judgment value by the exhaust pressure coefficient.
In short, an exhaust pressure coefficient xcex11 corresponding to the ash accumulated estimation value SAsh=xcexa3(Ashxc3x97xcex94t) is calculated, the reference judgment value xcex94Pe0, Pe0, Re0 is multiplied by the exhaust pressure coefficient xcex11 to determined the value of xcex11xc3x97xcex94Pe0, xcex11xc3x97Pe0, xcex11xc3x97Re0 and the reference judgment value xcex94Pe0, Pe0, Re0 is replaced, by the value, to correct.
4) The aforementioned DPF unit, wherein the regeneration control means is configured to calculate the reference judgment value, from the torque of an engine and the engine speed, of the time when the exhaust pressure for judging the regeneration start timing is measured by an exhaust pressure sensor.
In the calculation of the reference judgment value xcex94Pe0, Pe0, Re0 also, the reference judgment value xcex94Pe0, Pe0, Re0 for judging the regeneration start timing concerning the operation state of an engine presenting an engine torque Q and an engine speed Ne is obtained beforehand by experiment or computation, they are prepared as map data Mxcex94pe0 (Q, Ne), Mpe0 (Q, Ne), Mre0 (Q, Ne) or function fxcex94pe0(Q, Ne), fpe0(Q, Ne), fre0(Q, Ne), and they are used.
The regeneration control method of the DPF unit for achieving the aforementioned first object is configured as follows.
1) In a diesel particulate filer unit comprising a filter for capturing particulates in the exhaust gas of a diesel engine, exhaust pressure sensors disposed in an exhaust passage, and a regeneration control means for starting the regeneration operation of said filter, according to the judgment results based on the comparison between the exhaust pressure measured by the exhaust pressure sensors and a predetermined exhaust pressure judgment value, and regenerating said filter by removing particulates captured by said filter through combustion or chemical reaction by a catalyst, the ash accumulated quantity of ash leaked into the exhaust gas and accumulated in said filer is estimated and said exhaust pressure judgment value for judging the regeneration operation start based on an ash accumulated estimation quantity is corrected.
2) The regeneration control method of the aforementioned DPF unit, configured to calculate the ash quantity accumulated in said filter during an engine operation state, from the torque of an engine and the engine speed, and to calculate the ash accumulated estimation value, through the cumulative computation of the calculated ash quantity.
3) The regeneration control method of the aforementioned DPF unit, configured to calculate an exhaust pressure coefficient corresponding to the ash accumulated estimation value, and correcting the exhaust pressure judgment value, to a value determined by multiplying the reference judgment value by the exhaust pressure coefficient.
4) The regeneration control method of the aforementioned DPF unit, configured to calculate the reference judgment value, from the torque of an engine and the engine speed, of the time when the exhaust pressures for judging the regeneration start timing are measured by exhaust pressure sensors.
According to the DPF unit of the aforementioned composition and the regeneration control method of the same, the following functional effects can be obtained.
The effect of accumulation in the filter of ash left after the combustion of lubricant oil leaking from the cylinder of an engine into the exhaust gas is reflected on the judgment of regeneration start timing, because the exhaust pressure judgment value to be used for judging the regeneration operation start is corrected or compensated with the accumulated estimation value (deposit calculated value) of the lubricant oil, all the way estimating the state of accumulation and deposit on the filter of ash left after the combustion of lubricant oil of the engine. As the result, the judgment of regeneration start timing is performed always appropriately.
Then, the ash quantity accumulating in the filter is calculated from the torque of the engine and the engine speed, using the relation between torque of the engine and engine speed and ash accumulation quantity, determined beforehand through experiment or computation, and the ash accumulated estimation value can be estimated correctly by a simple algorithm, by calculating the accumulated estimation value through a cumulative computation of the ash quantity.
In addition, for the correction of exhaust pressure judgment value, as an exhaust pressure coefficient corresponding to the accumulated estimation value is calculated, and the exhaust pressure judgment value is corrected to a value determined by multiplying the reference judgment value by the exhaust pressure coefficient, the operation for reflecting the effect of lubricant oil on the judgment of regeneration start timing becomes an extremely simple computation.
Moreover, as the reference judgment value is calculated from the torque of engine and the engine speed of the time when the exhaust pressure for judging the regeneration start timing, using the relation between torque of the engine and engine speed and ash accumulation quantity, determined beforehand through experiment or computation, and the exhaust pressure judgment value is calculated from the reference judgment value, the measured exhaust pressure and the exhaust pressure judgment value for comparison judgment result in being able to be compared one the other for the operation state of a same engine. Consequently, the difference of exhaust pressure due to the difference of operation state of the engine is cancelled, the judgment of regeneration start timing can be performed more finely and appropriately.
As a result, the regeneration start timing of the filter of the DPF unit can be judged correctly, even when the mileage of a diesel engine vehicle having the DPF unit on board. Consequently, it can travel removing the PM efficiently by preventing the filter from clogging.
Moreover, a DPF unit for achieving the second object is configured as follows.
1) A continuous regeneration type diesel particulate filer unit comprising a filter with catalyst for capturing particulates in the exhaust gas from a diesel engine and, burning the captured particulates by catalytic action, wherein an oxidation catalyst is disposed upstream the filter with catalyst, for raising the exhaust gas temperature through oxidation of HC and CO in the exhaust gas.
According to the configuration, the oxidation catalyst disposed upstream the continuous regeneration type filter with catalyst can oxidize carbon monoxide (CO) and unburned fuel (HC) or the like in the exhaust gas, for raising the exhaust gas temperature flowing into the filter with catalyst. Therefore, the temperature of the filter with catalyst can raise even in an engine operation state at a relatively low exhaust gas temperature, allowing to burn and remove particulates (the PM) being captured.
Then, in a normal operation, during an operation state (A) of an engine of low revolution speed, the PM are burned and removed by raising the exhaust gas temperature, through execution of fuel injection control such as retard operation of main injection timing and post injection or the like, as mentioned below, when the filter with catalyst comes to be clogged.
2) The aforementioned continuous regeneration DPF unit comprising a regeneration control means for performing a regeneration processing against the clogging of said filter with catalyst and, wherein said regeneration control means is configured to activates said oxidation catalyst by raising the exhaust gas temperature through fuel injection control of an engine, during regeneration of said filter with catalyst under an engine operation condition where the exhaust gas temperature of the engine is lower than the activation temperature of said oxidation catalyst, for burning and removing particulates captured by said filter with catalyst.
According to the configuration, the exhaust gas temperature raises, the oxidation catalyst is activated and the temperature of exhaust gas passing through the oxidation catalyst raises furthermore, through execution of fuel injection control such as retard operation of main injection timing and post injection or the like, even in an operation state of an engine of low torque and low revolution speed, where the exhaust gas temperature is low, and the captured particulates can not be burned and removed, by a continuous regeneration type DPF unit of the related art.
Therefore, the temperature of the filter with catalyst raised, and particulates captured by the filter with catalyst are burned and removed by catalytic action of the filter with catalyst. Consequently, the filter with catalyst is not clogged even during a prolonged idling operation, a low speed operation, or a downhill traveling operation where the engine brake is activated, allowing to capture continuously particulates in the exhaust gas.
On the other hand, as combustion of particulate is made to be controlled by controlling the exhaust gas temperature through retard operation of main injection timing or post injection of fuel injection, without using a heating heater, the fuel injection comes to be performed by a fuel injection control unit which is already installed. Consequently, it becomes unnecessary to install additionally a heater for heating, a power supply, or other new equipment or new control units, allowing to make the whole unit compact. Consequently, it results in an unit that can be attached simply to a vehicle.
3) The aforementioned continuous regeneration type DPF unit, configured to raise the exhaust gas temperature by said fuel injection control in multiple stages equal or superior to two stages.
According to the configuration, the exhaust gas temperature is raised in multiple stages equal or superior to two stages, preventing an uncontrolled combustion from occurring when the PM accumulated in the filter with catalyst burns suddenly in a manner of chain reaction, and avoiding damage of the filter with catalyst when its temperature becomes equal or superior to the fusion damage temperature.
4) Also, the aforementioned continuous regeneration type DPF unit, wherein said fuel injection control is configured to comprise, at least, either one of retard operation of main injection or post injection operation.
According to the configuration, as retard operation of main injection and post injection operation are adopted as fuel injection control, one can cope only by changing the program of an existing fuel injection control unit, and the filter regeneration becomes possible relatively simply even in a low torque, low revolution speed area of an engine.
In addition, the regeneration control method of the continuous regeneration type DPF unit for achieving the aforementioned second object is configures as the following method.
1) In a continuous regeneration type diesel particulate filer unit formed by comprising a filter with catalyst for capturing particulates in the exhaust gas from a diesel engine and, burning the captured particulates by catalytic action, and an oxidation catalyst disposed upstream the filter with catalyst, for raising the exhaust gas temperature through oxidation of HC and CO in the exhaust gas, a method configured to raise the exhaust gas temperature through fuel injection control of the engine, during the regeneration of said filter with catalyst under an engine operation condition where the exhaust gas temperature of the engine is lower than the activation temperature of said oxidation catalyst, in order to burn and remove particulates captured by said filter with catalyst.
According to the aforementioned method, the exhaust gas temperature raises, the oxidation catalyst is activated and the captured particulates are burned and removed by catalytic action of the filter with catalyst, through execution of fuel injection control such as retard operation of main injection timing and post injection or the like, in an operation state of an engine of low torque and low revolution speed, where the exhaust gas temperature is low, the oxidation catalyst is poorly active, and the captured particulates can not be burned and removed, by a regeneration control method for continuous regeneration type DPF unit of the related art. Therefore, the filter with catalyst is not clogged even during idling operation, low speed operation, or such a downhill traveling operation that the engine brake is activated, allowing to capture continuously particulates in the exhaust gas.
2) The regeneration control method of the aforementioned continuous regeneration type DPF unit, configured to raise the exhaust gas temperature by said fuel injection control in multiple stages equal or superior to two stages.
According to the method, the exhaust gas temperature is raised in multiple stages equal or superior to two stages, preventing the PM accumulated in the filter with catalyst from burning suddenly in a manner of chain reaction, and damaging the filter with catalyst when its temperature becomes equal or superior to the fusion damage temperature.
3) The regeneration control method of the aforementioned continuous regeneration type DPF unit, wherein said fuel injection control is configured to comprise, at least, either one of retard operation of main injection or post injection operation.
According to the method, as retard operation of main injection and post injection operation are adopted as fuel injection control, one can cope only by changing the program of an existing fuel injection control unit, and the filter with catalyst can be regenerated relatively simply even in a low torque, low revolution speed area of an engine.
4) The regeneration control method of the aforementioned continuous regeneration type DPF unit, configured to raise at first the exhaust gas temperature through retard operation of fuel main injection and to raise further the exhaust gas temperature, by adding the fuel post injection operation, when the temperature of the exhaust gas flowing into said filter with catalyst attains a predetermined first target temperature value.
According to the method, the exhaust gas temperature is raised through retard operation of main injection timing for preheating the oxidation catalyst, during the start of regeneration mode operation, and after activation of the oxidation catalyst, the post injection is performed, allowing to prevent white smoke from generating, which otherwise tends to generate during the regeneration start.
5) The regeneration control method of the aforementioned continuous regeneration type DPF unit, configured to further raise the exhaust gas temperature, by increasing the injection quantity of fuel post injection, after the temperature of the exhaust gas flowing into said filter with catalyst attains a predetermined second target temperature value by a post injection of fuel of a given quantity, during said fuel post injection operation.
According to the method, a sudden temperature elevation due to a sudden combustion of deposited the PM in a chain reaction manner can be prevented, and the fusion damage of the filter with catalyst can be avoided, because the temperature of exhaust gas entering the filter with catalyst in two stages or multiple stages.
6) The regeneration control method of the aforementioned continuous regeneration type DPF unit, configured to estimate the quantity of particulate to be accumulated in said filter with catalyst during the operation of an engine and the quantity of particulate to be burned and removed from the operation state of the engine, calculate the accumulated estimation value of particulate by cumulative computation, and to judge the regeneration start by using whether the accumulated estimation quantity of the particulate has exceeded a predetermined accumulation quantity or not.
According to the method, as the regeneration mode operation can be entered, when the accumulated estimation quantity of particulate has exceeded the predetermined accumulation quantity, along with the estimation computation of accumulation state of the particulate, the regeneration of filter with catalyst can be performed with an optimal timing.
Therefore, the particulate can be captured, burned and removed efficiently, all the way preventing the fuel efficiency from deteriorating.